Monopole antenna with adjustable loading coil



Nov. 24, 1970 G. M. WENDELL MONOPOLE ANTENNA WITH ADJUSTABLE LOADING COIL Filed March '7, 1968 FIG. 1

I INVENT OR GORDON M. WENDELL @TORNEY Y United States Patent O US. Cl. 343-750 2 Claims ABSTRACT OF THE DISCLOSURE A metal whip or rod carries at its lower end a ferrite core which is adjustable axially in a dielectric sleeve that is surrounded by a wire coil. The coil is connected at its lower end to a metal conducting tube. The dielectric sleeve is fastened on the upper end of this metal tube. The whip or rod is adjustable axially in a metal bushing which is secured in the upper end of the sleeve. The upper end of the coil is connected to this bushing. A set screw, threaded through the bushing, holds the whip or rod in any adjusted position.

This invention relates to radio antennas, and more particularly to an antenna particularly adapted for use with citizen band radios. The invention has, however, wide application, and is applicable to vertical antennas, parasitic beam antennas, and dipole antennas in HF, VHF and UHF spectrum.

Because normal citizen band radios operate at very high frequencies, and on relatively low power inputs, it is desirable that the antennas for such radios be adjustable to compensate for changing weather conditions, varying inductance conditions in the antennas themselves, etc. Also, particularly in the case of automobile antennas, which are employed with citizen band radios, it is desira ble that the antennas be sturdy and compact. A major disadvantage of prior such antennas is that they have had to be extremely long to tune the coupled radios for various Wave lengths. Consequently, when used on automobiles, they are often damaged by low-hanging objects. Further than this, in any use, they are cumbersome to mount and subject to wind-whipping and breakage.

It is an object of this invention to provide an improved antenna of the type described, which is sturdier and more compact than prior, such antennas.

Another object of this invention is to provide an antenna of the type described, which is simple in construction, yet readily adjustable or tunable for different wave lengths.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawing.

In the drawing:

FIG. 1 is an elevational view of an antenna made according to one embodiment of this invention, parts thereof being cut away and shown in section; and

FIG. 2 is a sectional view taken along the line 22 in FIG. 1 looking in the direction of the arrows.

Referring now to the drawing by numerals of reference, denotes the improved antenna generally; and 12 designates a Plexiglass or like insulating sleeve 12, which is carried on the upper end of an elongate, metal conductor tube 14 coaxially thereof. Secured in the upper end of sleeve 12 coaxially thereof, and projecting above the sleeve, is a metal bushing 16. Helically coiled around the outside of sleeve 12 is an electric wire coil 18. The lower end of this coil is secured by a jumper 19 to the upper end of conductor tube 14; and the upper end of the coil is connected by a jumper 20 to bushing 16. Coil 18 and the sleeve 12 are enclosed or embedded in a generally 3,543,275 Patented Nov. 24, 1970 ICC cylindrical, plastic insulating sleeve 22, the upper end of which surrounds the bushing 16 coaxially thereof, and the lower end of which is secured to and surrounds the upper end of the tube 14 coaxially thereof.

Axially slidable in a bore 24 in the bushing 16 is an adjustable, metal Whip or rod 26. The lower end of rod 26 extends into the bore in the sleeve 12, and has secured thereto a cylindrical, ferrite core 28, which has a diameter less than the inner diameter of sleeve 12. A set screw 30, which threads through the sleeve 22 and bushing 16, frictionally engages rod 26 releasably to secure the rod and the core 28 against axial movement in any adjusted position of the rod.

In use the antenna 10 is mounted with the lower end of its tube 14 connected by conductor 32 to a transmitter T, which is shown schematically in box form in FIG. 1. To tune the antenna 10 for a particular frequency, the setscrew 30 is loosened, and the rod 26 and its core 28 are adjusted axially in coil 18 to effect change in the inductance of coil 18. When the desired tuning has been achieved, setscrew 30 is tightened to secure rod 26 in adjusted position.

From the foregoing it will be apparent that applicant has developed a particularly sturdy and reliable antenna, particularly useful as a vertical antenna in conjunction with a citizen band radio, but having utility also in the high frequency (HF), very high frequency (VHF) and ultra high frequency (UHF) spectrum. The features dis closed herein may also be incorporated in parasitic beam antennas, and also in dipole antennas. Moreover, although in the embodiment illustrated the antenna is specifically associated with a transmitter T, it will be apparent that it would be equally useful with a radio receiver.

While the invention has been described in connection with a specific embodiment thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention, including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. An antenna, comprising:

a first dielectric sleeve,

an electric wire coil wound around said first sleeve,

a second dielectric sleeve surrounding said coil and said first sleeve coaxially thereof, and extending axially beyond opposite ends of said first sleeve,

a first tubular cylindrical conductor secured at one end thereof in one end of said second sleeve in electrical connection with one end of said coil,

a metal bushing secured in the opposite end of said second sleeve in electrical connection with the opposite end of said coil, and having an axial bore communicating with the bore of said first sleeve,

a second conductor slidably adjustable axially in the bore of said bushing in electrical contact therewith and projecting at one end into the bore in said first sleeve,

a ferrite core secured to said one end of said second conductor for axial adjustment with said second conductor in the bore of said first sleeve to vary the inductance of said coil, and

a manually adjustable locking member mounted on said bushing for movement selectively into and out of a locking position in which it engages said second conductor releasably to secure the latter against axial movement relative to said bushing.

2. An antenna as defined in claim 1, wherein said locking member comprises a set screw adjustably threaded in a radial hole in said bushing to engage at its inner end with said second conductor, when said screw is in its locking position.

References Cited UNITED STATES PATENTS 2,931,034 3/ 1960 Harrison et a1 343-750 3,104,394 9/ 1963 Yokoyama 343-750 4 3/1965 Senrui 343-749 8/1966 Nuttle 343-750 US. Cl. X.R. 

